Glass-fiber containing composite materials for alkali metal-based batteries and methods of making

ABSTRACT

Glass-fiber composites are described that include a substrate containing glass fibers and particles in contact with the glass fiber substrate. The particles may include an alkali-metal containing compound. In addition, batteries are described with an anode, a cathode, and an electrolyte. The cathode may include alkali-metal containing nanoparticles in contact with glass fibers. Also describe are methods of making a glass-fiber composite. The methods may include the steps of forming a wet laid non-woven glass fiber substrate, and contacting alkali-metal containing particles on the substrate.

BACKGROUND OF THE INVENTION

Lithium-ion batteries have gained widespread adoption in portableelectronic devices, and are increasingly being used in larger-scalesystems such as hybrid and electric vehicles and power generationsystems. However, attempts to scale lithium-ion battery technology tothese larger applications has exposed a number of problems.

First, the cost of lithium is high compared to conventional nickel,cadmium and lead based battery technologies, and these costs aremagnified for larger sized batteries. Thus, there is a need for reducingor eliminating the about of lithium used in the battery. The relativelylow proven reserves of lithium in the United States may also limitLi-based battery development and production in that country.

Second, there are safety concerns with some types of lithium batterytechnology that may be more prone to explosions and fires when scaled tolarger sizes. For example, lithium-based batteries that uselithium-cobalt (LiCoO₂) cathodes can sometimes experience a release ofoxygen during intense and/or frequent electrical charging anddischarging cycles. The released oxygen is combustible, and can reactwith other components in the battery to create a fire or explosion.

Partly in response to the safety concerns with lithium-cobalttechnology, other lithium-based materials have been examined for batteryapplications. One of these compounds is lithium iron phosphate(LiFePO₄). However, bulk LiFePO₄ has proven to have relatively slow massand charge transport properties, resulting in relatively poor batterypower output. Sol-gel processes used to make LiFePO₄ materials forbatteries are also inefficient and expensive, further increasing thecost of these batteries. Thus, there is a need for new approaches tomaking Li-based batteries and their components with improved performanceand reduced cost.

BRIEF SUMMARY OF THE INVENTION

Materials are described that can improve the performance and reduce thecost of Li-based batteries. These materials include glass-fibers thatcan be fashioned into a non-woven mat that acts as a substrate forLi-containing nanoparticles. The mat provides strong,dimensionally-stable, a high-surface area scaffold for thenanoparticles, which provides a large surface area of active sites whilereducing the amount of lithium left in the bulk. This means less lithiumis required for an equivalent energy density, power density, etc., thanused in conventional Li-ion materials. They may also enhance the massand charge transport properties of Li-based compounds such as LiFePO₄.

Also described are sodium glass fibers that may eliminate the need forlithium altogether in specific battery components such as the cathodeelectrode. Sodium-based compounds such as sodium iron flourophosphate(Na₂FePO₄F) have been discovered that have ion transport ratescomparable or exceeding Li-based compounds. Some of these sodium-basedcompounds can be incorporated into sodium glass fibers, which makes thefibers themselves the active material for ion transport and eliminatesthe need for additional nanoparticles to be added (although there is noprohibition against adding nanoparticles, which in some instances mayfurther enhance the material's performance). These sodium glass fibersmay be used to make a lithium free cathode.

Embodiments of the invention include glass-fiber composites that includea substrate containing glass fibers and particles in contact with theglass fiber substrate. The particles may include an alkali-metalcontaining compound, such as a lithium-containing compound.

Embodiments of the invention further include substrates having glassfibers made from sodium-containing materials, such as Na₂FePO₄F. Theglass fibers may be microfibers and/or nanofibers.

Embodiments of the invention may also include batteries having an anode,a cathode, and an electrolyte. The cathode may include alkali-metalcontaining nanoparticles in contact with glass fibers.

Embodiments of the invention may also further include batteries having acathode that includes glass microfibers which include Na₂FePO₄F,

Embodiments of the invention may still further include methods of makinga glass-fiber composite. The methods may include the steps of forming awet laid non-woven glass fiber substrate, and contacting alkali-metalcontaining particles on the substrate.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the invention. The features and advantages ofthe invention may be realized and attained by means of theinstrumentalities, combinations, and methods described in thespecification.

DETAILED DESCRIPTION OF THE INVENTION

Glass fiber composites are described that may be used as electrodes inelectrical storage batteries, among other devices and applications.Examples of the composites include non-woven glass microfibers thatprovide a durable, dimensionaily stable, microporous substrate foralkali-metal containing nanoparticles, such as lithium and/orsodium-containing nanoparticles. Specific examples of thesenanoparticles may include lithium iron phosphate (LiFePO₄) and sodiumiron fluorophosphate (Na₂FePO₄F) nanoparticles.

Also described are glass fiber substrates made from glass fibers thatincorporate sodium iron fluorophosphates. Making the glass fibers out ofNa₂FePO₄F may obviate the need to introduce nanoparticles to the fiberswhen forming an electrode. These fibers may have micro- and/ornano-sized diameters that are similar or the same as the scale of thenanoparticles.

The composites may be made by combining a wet laid non-woven gas-fibersubstrate with the nanoparticles. The nanoparticles may be introduced tothe substrate by among other methods, coating, embedding, or saturatingthe nanoparticles in the substrate.

Both the above-described materials may be formed into a cathodeelectrode of an electrical storage battery. The cathode may be separatedfrom the anode electrode by an electrolyte. The electrolyte may be, forexample, a micro-porous separator membrane that contains LiPF6, and theanode electrode may be a metallic anode such as a lithium metal anode oran alloy of two or more metals.

Structural cathodes made from the composite materials have increasedsurface area for holding the nanoparticles, and may be incorporated intolarger, more reliable cells having reduced winding costs. Thehigh-surface area glass fiber substrates may include substrates withsurface areas ranging from about 20 m²/g to about 300 m²/g or more.

Increasing the accessible surface area of the cathode can increase theion mass transfer through the cathode as well as the total energydensity of the cathode and battery. The present cathodes may includehierarchically porous structures that combine micro- and nanoscale poresto increase the structural integrity and surface area of the cathodematerial. Batteries that include the present cathodes may achieve poweroutputs of 760 W/kg or more, and energy densities of about 100 mAh/g ormore. The batteries can also have improved cycle performance with lossesof about 3% or less over about 700 cycles.

The composite materials have high-surface area produced by forming theglass mircofibers and/or nanofibers into strong, durable, non-wovenmats. The fiberglass mats may be fashioned into a micro- and/ornanoporous substrate. They may provide improved mechanical and thermalproperties, as well as improved dimensional stability during electricalcharging and discharging. This can increase the overall life span ofbatteries made with these materials. The increased strength of thesecomposite materials also allows more rapid winding of cells and canincrease the size of the cells, both of which can lower manufacturingcosts of the batteries.

Batteries made with the present glass fiber materials (either with orwithout nanoparticles) may have a number of advantages over currentlithium-ion battery technology. These advantages may include:

Specific Energy Density (Wh/kg)—The present batteries can meet or exceedabout 200 Wh/kg (system) and about 400 Wh/kg (cell).

Volumetric Energy Density (Wh/I)—The increased strength provided by theglass fiber substrate allow tighter packing of the battery electrodesand separator. The nanoporous electrodes allow the electrolyte topenetrate into the electrodes, thus creating an efficient utilization ofspace. Sodium glass (e.g., Na₂FePO₄F) cathodes may have a lowerintrinsic power density than cathodes using lithium-containingnanoparticles, but because active areas of the sodium glass cathodesinclude the fibers themselves, there is less inactive area for thesecathodes.

System Cost (kWh/$)—For sodium glass cathodes, cost reductions may berealized due to the decreased use of lithium. These cathodes can reducecosts to about US$250/kWh or less. For cathodes that includeLi-containing nanoparticles cost reductions of about 20% to about 40%compared to conventional Li-ion batteries may be realized from thereduction in cell windings and increased cell size.

Specific Power Density (W/kg)—Nanoscale systems can increase powerdensity at high discharge rates owing to their increased ion masstransfer. The present batteries may have power densities of about 760W/kg and energy density of about 100 mAh/g. The present materials mayalso be incorporated into system features such as ultracapacitors thatcan boost power in pulses.

Volumetric Power Density (W/I)—Cathodes made from the present materialscan have improved high-drain performance.

Cycle Life (#)—Batteries may achieve about 1000 or more cycles. Bindingmaterials and techniques are employed to reduce the unbinding ofnanoparticles from the glass-fiber substrate in those embodiments wherenanoparticles are used. For sodium-glass cathodes that do not have boundnanoparticles, even larger numbers of cycles may be achieved.

Round Trip Efficiency—The present batteries may have discharge capacitylosses of about 3% or less over 700 cycles at a rate of 1.5 C. At C/3,the capacity loss may be significantly lower,

Temperature Tolerance—The present composites, substrates, cathodes, andbatteries may have maximum operating temperatures of about 65° C. ormore.

Self Discharge—The present materials may be optimized to reduce the selfdischarge rate to what is comparable in conventional Li-ion batteries.

Safety—The present materials include phosphate containing activeelectrode materials. Phosphates (—PO₄) typically have more tightly boundoxygen groups than other conventional electrode materials (e.g.,LiCoO₂). This reduces the risk of oxygen liberation that can contributeto fires and explosions in the phosphate-containing batteries andsystems. The strength and stability of the glass-fiber substrate canalso reduce the incidents of short circuits in the battery and othercatastrophic failure modes.

Calendar Life (Years)—The glass fiber substrates do not interfere withbattery operation and iron-phosphate systems have significantly lowerdegradation rates than conventional Li-ion batteries and systems. Thepresent batteries may have an increased lifetime compared to the averagelifetime for a conventional system.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent invention. Accordingly, the above description should not betaken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the electrode” includesreference to one or more electrodes and equivalents thereof known tothose skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

What is claimed is:
 1. A glass fiber substrate comprising glass fibersthat include Na₂FePO₄F.
 2. The glass fiber substrate of claim 1, whereinthe glass fibers comprise nanofibers.
 3. The glass fiber substrate ofclaim 1, wherein the glass fibers comprise non-woven glass microfibers.4. A glass-fiber composite comprising: a substrate comprising glassfibers, wherein the glass fibers comprise Na₂FePO₄F; andlithium-containing nanoparticles bound to a surface of the glass fibers.5. The composite of claim 4, wherein the glass fibers comprise non-wovenglass microfibers.
 6. The composite of claim 4, wherein thelithium-containing nanoparticles comprise LiFePO₄.
 7. The composite ofclaim 4, wherein the glass-fiber composite comprises a cathode of abattery.
 8. The composite of claim 4, wherein the glass fibers comprisenanofibers.
 9. A battery comprising: an anode; a cathode that includesglass fibers comprising Na₂FePO₄F; and an electrolyte.
 10. The batteryof claim 9, wherein the glass fibers comprise glass nanofibers.
 11. Thebattery of claim 9, wherein the cathode comprises LiFePO₄.
 12. Thebattery of claim 9, wherein the anode comprises lithium metal.
 13. Thebattery of claim 9, wherein the electrolyte comprises a microporousseparator membrane containing LiPF₆.
 14. A battery comprising: an anode;a cathode comprising lithium-containing nanoparticles bound to a surfaceof glass fibers, wherein the glass fibers comprise Na₂FePO₄F; and anelectrolyte between the anode and the cathode.
 15. The battery of claim14, wherein the lithium-containing nanoparticles comprise LiFePO₄. 16.The battery of claim 14, wherein the anode comprises lithium metal. 17.The battery of claim 14, wherein the electrolyte comprises a microporousseparator membrane containing LiPF₆.